Although many friends say that you should just listen to the temperature ratings of sleeping bags but not take them seriously, others suggest adding 3–5 degrees to the rating to ensure a good night’s sleep. I’ve also heard people claim that certain brands’ ratings are inaccurate and shouldn’t be trusted. But I think the concept of temperature ratings is still quite unclear to most people. Moreover, when you look at the product descriptions of some sleeping bags, you might see one rating sometimes, two at other times, and then suddenly another brand displays three ratings—which can be even more confusing. And if someone tells you there are even four ratings? Isn’t that just dizzying?
If you don’t know what these temperature ratings actually mean, then let me explain today the internationally recognized EN13537 testing method and its interpretation of temperature ratings. The reason I’m using the European standard for explanation is simply because China doesn’t have an officially recognized temperature rating standard. (And if you’re indignant and point out that some sleeping bags use military testing standards, please note what I said earlier—I’m referring to nationally accredited testing standards, and unfortunately, China currently doesn’t have such standards, including any so-called military lab testing protocols for sleeping bags.) Nowadays, whether it’s TNF, MHW, or supermarket-brand Decathlon, everyone uses the EN13537 standard for sleeping bag temperature ratings. So first, let me explain what these four temperature ratings mean according to this standard:
MAXIMUM (Upper Limit): The upper limit of the high-temperature comfort range is determined under standard test conditions with a standard healthy male subject. The test assumes that the sleeper does not cover the upper body with the sleeping bag and does not sweat excessively.
COMFORT (Comfort Temperature): Determined under standard test conditions with a standard healthy female subject in a relaxed state. She should not feel cold (i.e., no shivering), and should remain comfortable throughout the night.
LIMIT (Lower Limit): Determined under standard test conditions with a standard healthy male subject curled up in the sleeping bag. He should not shiver and should remain comfortable throughout the night.
EXTREME (Extreme Low Temperature): Determined under standard test conditions with a standard healthy female subject exposed to severe cold (with shivering). At this point, there is a risk of hypothermia or even death. The extreme temperature is a theoretical limit, considered only as a dangerous critical point that is very difficult to reach.
Many factors that affect sleep quality are not included in EN13537, such as external elements like strong winds, humidity, sleeping pad thickness, and clothing layers—all of which can influence comfort. Personal factors like hunger, fatigue, and environmental adaptability also significantly impact sleep quality. Another important factor is localized discomfort—like waking up with a cold face because your sleeping cap slipped off, or having your feet exposed to the freezing ground outside the pad—these common issues can all affect the quality of your night’s sleep.
Please note that EN13537 specifically states afterward that external influences can affect the validity of the sleeping bag’s temperature ratings. Additionally, since EN13537 uses mannequins to generate test data, it eliminates the instability caused by individual differences in human physiology or constitution. Whether the European testing standard is scientific or suitable for Chinese people is another question, but in the absence of a Chinese national standard, at least it gives us a basic understanding of the environments in which sleeping bags can be used. Also, I personally believe it’s very important that you can compare temperature ratings across different products to help you make choices—of course, provided those ratings are all tested under the same standard, i.e., using the EN13537 method. The reason I emphasize the same standard is that I know that, in China, the vast majority of sleeping bag temperature ratings are estimated rather than tested. I’m not just making this up—the current state of China’s sleeping bag industry is just like that. Because sending products to Europe for testing is really expensive. Heh.
Finally, I really want to remind fellow travelers to pay attention to this: many sleeping bags indicate their EXTREME LOW temperature rating, and I think this is a highly irresponsible way to label temperature ratings. (Refer to the above for the explanation of extreme low temperature.) Please pay attention to the comfort levels of the different ratings in the future, and don’t obsess over the extreme ratings—they are just theoretical values.